Optoelectronic devices such as organic light emitting diodes (OLEDs) are being increasingly employed for lighting and display applications. The OLED includes a stack of thin organic layers disposed between two charged electrodes (anode and cathode). The organic layers may include a hole injection layer, a hole transport layer, an emissive layer, an electron transport layer, and an electron injection layer. Upon application of an appropriate voltage to the OLED lighting device, the injected positive and negative charges recombine in the emissive layer to produce light.
Typically, the light emitted by the emissive layer may transmit away from the emissive layer and out of the OLED to be viewed by a user and/or used by the optoelectronic device for various lighting or display applications. However, not all of the light emitted by the emissive layer may transmit out of the OLED. For example, some light (e.g., 20% in conventional OLEDs) may be trapped in various layers of the OLED, thereby decreasing the efficiency of the device, as not all of the light emitted by the emissive layer is utilized. Such inefficiencies may translate into higher operating power requirements and/or shorter lifespan of the device as the application of higher voltages may be necessary to obtain a desired luminescence of the OLED.
Some attempts at increasing the efficiency of the OLED include manipulating the layers of the OLED to increase the light emitted out of the device. For example, some techniques involve optimizing the thickness and possibly the refractive indexes of the OLED layers (commonly referred to as optimizing the OLED cavity), or incorporating scattering particles in the OLED layers to increase the scattering of otherwise trapped light out of the OLED.